Killjoy is boring drunk, having ejected one Republican (6)
I believe the answer is:
'killjoy' is the definition.
'is boring drunk having ejected one republican' is the wordplay.
I cannot quite understand how this works, but
'is' is found in the answer.
'one' could be 'er' (I've seen this in other clues) and 'er' is found within the answer.
The remaining letters 'my' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
(Other definitions for misery that I've seen before include "Feeling of great unhappiness" , "Party-pooper" , "Torment" , "Great suffering" , "Wretched conditions" .)